The invention relates generally to steam turbines with drum rotors and more specifically to cooling for the drum rotor.
Advanced combined-cycle power plants rely on higher steam temperatures to operate at peak efficiency. High reaction designs using drum rotor construction must be able to withstand higher steam temperatures without compromising rotor life. One solution is to use better, more temperature-resistant, rotor materials. A less costly solution may be to cool the rotor with low temperature steam.
FIG. 1 illustrates a longitudinal cross-sectional view of a steam turbine 5 with a drum rotor 10 and a turbine casing 15 with multiple stages 16, 17, 18, 19, 20 comprised of alternating rows of stator vanes 25 extending inward radially from the turbine casing 15 and rotor blades 26 of rotor buckets 24 where the blades extend outward radially from male dovetailed roots 27 mounted in tangential female dovetail slots 30 cut around the periphery of the drum rotor 10. Working steam 21 flows from steam inlet 22 sequentially through the stages 16, 17, 18, 19, 20 of the alternating stator vanes 25 and rotor blades 26 causing steam temperature and pressure to decrease. The initial stages of the drum rotor 10 are thus exposed to the highest temperature and pressure steam. A packing head 28 seals the end of drum rotor 10 with packing elements 29.
In one prior art approach, external cooling steam 35 is delivered to the drum rotor 10 from an external source 36, as illustrated in FIG. 2. Here, the external source 36 may make use of a snout 37, which penetrates the turbine casing 15. The snout is shown here entering the packing head 28. One or more snouts may be used. The external cooling steam 35 is fed through a passage. The packing head 28 could be designed such that passage is a straight radial hole. Alternatively, the packing head 28 could be designed as an assembly to enable a more complicated passage. The cooling steam 35 is delivered to an outlet 39 and fills an annulus 40. A labyrinth seal, brush seal, or other seal type or combination of seals is employed at locations 41A and or 41B to restrict the leakage of cooling steam 35 into the working steam flow path 21. FIG. 17 illustrates an expanded view of seal arrangements 41 that restrict leakage of the cooling steam into the working steam flow path.
While the path shown in FIG. 2 will provide coolant to the forward side of stage 1 16, it is often necessary to cool multiple stages. Axial steam flow through the drum rotor 10 may be enabled by passages created by axial grooves 44 in the roots of buckets 24 as illustrated in FIG. 3.
Previous concepts have included axial holes 45 in the drum rotor, as illustrated in FIG. 4. Cooling steam 46 passes through the axial holes 45 to flood the circumferential space 48 between the tangential female dovetail slots 30 and the male dovetail roots 27 to reduce the rotor temperature. Unfortunately, long axial holes 45 in the rotor are currently very difficult to produce.
Accordingly, there is a need to provide an effective cooling steam flow path for multiple forward stages of a drum rotor in ways that may be applied with current technology and which do not weaken the rotor.